This is from the MACOSX_PORT JIRA:

Run this test application with a build of 7u4 (Mac OS X).

==================
import java.util.Properties;

public class MACOSX_PORT_515 {
    public static void main(String args[]) throws Exception {
        Properties p = System.getProperties();
        System.out.println("Got properties " + p);
        
        System.setProperties(null);
        
        Properties q = System.getProperties();
        System.out.println("Got properties " + q);

        System.setProperties(null);
    }
}
=================================

You will crash. The log shows the crashed thread is:

Thread 2 Crashed:
0 libsystem_kernel.dylib 0x00007fff96ed2ce2 __pthread_kill + 10
1 libsystem_c.dylib 0x00007fff942a27d2 pthread_kill + 95
2 libsystem_c.dylib 0x00007fff94293a7a abort + 143
3 libsystem_c.dylib 0x00007fff942f284c free + 389
4 libjava.dylib 0x00000001041a9a7f freeProps + 194
5 libjava.dylib 0x00000001041a21b0 Java_java_lang_System_initProperties + 9171
6 ??? 0x0000000104e34bd1 0 + 4376972241
7 ??? 0x0000000104e29173 0 + 4376924531
8 ??? 0x0000000104e28f98 0 + 4376924056
9 ??? 0x0000000104e28f98 0 + 4376924056
10 ??? 0x0000000104e28f98 0 + 4376924056
11 ??? 0x0000000104e28f98 0 + 4376924056
12 ??? 0x0000000104e29646 0 + 4376925766
13 ??? 0x0000000104e28f98 0 + 4376924056
14 ??? 0x0000000104e28f98 0 + 4376924056
15 ??? 0x0000000104e29646 0 + 4376925766
16 ??? 0x0000000104e28f98 0 + 4376924056
17 ??? 0x0000000104e29646 0 + 4376925766
18 ??? 0x0000000104e28f98 0 + 4376924056
19 ??? 0x0000000104e29646 0 + 4376925766
20 ??? 0x0000000104e28f98 0 + 4376924056
21 ??? 0x0000000104e29114 0 + 4376924436
22 ??? 0x0000000104e23438 0 + 4376900664
23 libjvm.dylib 0x00000001045671f7 JavaCalls::call_helper(JavaValue*, methodHandle*, JavaCallArguments*, Thread*) + 545
24 libjvm.dylib 0x0000000104566fd0 JavaCalls::call(JavaValue*, methodHandle, JavaCallArguments*, Thread*) + 40
25 libjvm.dylib 0x000000010457e7ca _ZL17jni_invoke_staticP7JNIEnv_P9JavaValueP8_jobject11JNICallTypeP10_jmethodIDP18JNI_ArgumentPusherP6Thread + 217
26 libjvm.dylib 0x0000000104577bec jni_CallStaticVoidMethod + 267
27 java 0x00000001040d07b0 JavaMain + 2988
28 libsystem_c.dylib 0x00007fff942a08bf _pthread_start + 335
29 libsystem_c.dylib 0x00007fff942a3b75 thread_start + 13
Link to the jira bug is: http://java.net/jira/browse/MACOSX_PORT-548